The present invention relates to surface-mounted antennas typically used in mobile communications systems such as mobile phones and short-distance wireless communications.
Frequencies in the UHF band and microwave band have been used exclusively for mobile communications systems such as mobile phones and short-distance wireless communications systems. Apparatuses used for these systems are required to cover a wide frequency band, be inexpensive, small, light and portable. Accordingly, a wide-band, high-gain, small, light, and inexpensive antenna is desired for these apparatuses.
One example of such antennas is a planar inverted-F antenna, as shown in FIG. 28, which employs a microstrip conductor. The antenna shown in FIG. 28 is a commonly adopted short antenna which is surface-mounted on a circuit board of an apparatus.
In this antenna, radiating element 100 made of plate conductor (hereafter, a planar radiating element is referred to as a radiating plate) and grounding plate 101 are disposed in parallel with a predetermined spacing, as shown in FIG. 28. In general, as shown in FIG. 28, grounding plate 101 is larger than radiating plate 100. A high frequency signal is supplied to a point (hereafter referred to as the feeding point) provided at a predetermined end of radiating plate 100 through feeding line 102. A point near the feeding point and grounding plate 101 are connected on radiating plate 100 by shorting plate 103 so as to ground at high frequencies. The name xe2x80x98inverted-F antennaxe2x80x99 is derived from the shape of this antenna as seen from the side.
The planar inverted-F antenna as configured above has an antenna radiating element on one face of grounding plate 101. Accordingly, the radiating element is seldom blocked by other components in an apparatus when the antenna is built into the apparatus. The planar inverted-F antenna is thus suitable for surface mounting in such apparatuses.
However, the antenna as configured above may have a narrower bandwidth when the spacing between radiating plate 100 and grounding plate 101 or a projected area of radiating plate 100 to grounding plate 101 is made small. These dimensions can thus be reduced by only a limited degree, making it difficult to further downsize and shorten the height of the antenna.
An object of the present invention is to offer a small and short antenna with a wider frequency band.
An antenna device of the present invention includes:
a radiating plate;
a grounding plate facing the radiating plate;
a feeding line disposed on a side or end of the radiating plate; and
a shorting portion which connects a point close to the feeding line and the grounding plate.
In addition, a slit is provided at a side or end at the side approximately opposing the feeding line. This causes two resonators to be formed on the radiating plate. The coupling level between these two resonators and positions of the feeder and shorting portion are adjusted.
The present invention has the following embodiments.
(1) The antenna can be downsized by forming an approximately T-shaped or tongue-shape slit to give each resonator a Stepped Impedance Resonator (SIR) structure.
(2) The antenna can be downsized by extending a part of the slit longer.
(3) The coupling level between two resonators is adjustable over a wider range by providing a conductive coupling plate so as to extend over the slit via an insulating member.
(4) The coupling level between two resonators is adjustable by partially changing the slit width.
(5) The coupling level between two resonators is adjustable by partially changing the size of the coupling plate.
(6) The antenna can be downsized and surface mounting is made feasible by forming the radiating plate and grounding plate respectively on the surface and rear face of the dielectric, magnetic substance, or a mixture of the two.
(7) The antenna radiating efficiency can be increased by providing air to the space between the radiating plate and grounding plate.
(8) The antenna can have a wider bandwidth and be downsized by forming plural independent slits.
(9) A change in the radiation resistance of the antenna can be flexibly matched by adding or forming a reactance element between a part of one or both of the two resonators and the grounding plate.
(10) The coupling level required for widening the antenna frequency band can be readily obtained by adding or forming a reactance element on a part of the slit.
(11) The reactance element is configured with a coupling plate, a comb element, microstrip line, chip capacitor, or chip inductor. This simplifies the antenna structure, and also enables matching large changes in the radiation resistance of the antenna.
(12) The coupling level between resonators is adjustable over a wider range by short-circuiting the coupling plate and at least one of two resonators.
(13) Variations in the antenna characteristics during manufacture can be suppressed by deforming the comb element using a laser or polisher to adjust the capacitance of the element.
(14) The slit is branched to form a rough T-shape about midway. At least one resonator has at least one of i) a capacitance element added to or formed on an area where a high-frequency electric field is dominant; and ii) an inductance element added to or formed on an area where a high-frequency magnetic field is dominant. This reduces the necessary circuit constant of element, resulting in reduction of the element size and loss in the element.
(15) The slit is branched to form a rough T-shape about midway, and at least one of the branched slits is bent approximately perpendicular near the side of the radiating plate toward the starting point of the slit. At least one resonator has at least one of i) a capacitance element added to or formed on an area where a high-frequency electric field is dominant, and ii) an inductance element added to or formed on an area where high-frequency magnetic field is dominant. This reduces the required circuit constant of element, resulting in reduction of the element size and loss in the element.
(16) The radiating plate is divided into two areas: An area where the starting point of the slit is present (first area), and an area where a shorting point or feeding point is present (second area). If the end point of the slit is present in the second area, the capacitance element and inductance element are respectively added to or formed on the first and second areas. This enables reduction of the required circuit constant of element, resulting in reducing the element size and loss in the element.
(17) The radiating plate is divided into two areas: An area where a starting point of the slit is present (first area), and an area where a shorting point or feeding point is present (second area). The slit is extended passing the second area and its end point lies in the first area. In this case, the capacitance element is added to or formed on the second area. This enables reduction of the required circuit constant of element, resulting in reducing the element size and loss in the element.
(18) The slit is branched to the first resonator side and the second resonator side about midway, and each branch is named the first slit and second slit. The radiating plate is also divided into an area where the starting point of the slit is present (first area) and an area where a shorting point or feeding point is present (second area). If the end point of the first slit is present in the second area, the capacitance element and inductance element are respectively added to or formed on the first and second areas in the first resonator. If the second slit is extended passing the second area and its end point is present in the first area, the capacitance element is added to or formed on the second area in the second resonator. This enables reduction of the required circuit constant of element, resulting in reducing the element size and loss in the element.
(19) At least one of the capacitance element and inductance element is added to or formed on at least one of a portion between the slits and a portion between the radiating plate and grounding plate. This achieves the required impedance characteristics for the resonator and the required coupling level between the resonators.
(20) The antenna can be downsized by adopting meander resonators.